CPR Chest Compression Monitor With Reference Sensor

ABSTRACT

Methods and devices for chest compression depth measurement for CPR.

This application is a continuation of U.S. application Ser. No.14/068,649, filed Oct. 31, 2013, now U.S. Pat. No. 9,220,443.

FIELD OF THE INVENTIONS

The inventions described below relate the field of CPR.

BACKGROUND OF THE INVENTIONS

Chest compressions provided as a component of cardiopulmonaryresuscitation (CPR) should be accomplished at a consistent depth ofabout 2 inches, according to the CPR Guidelines 2010. This is difficultto accomplish, especially over a long course of CPR. Chest compressionmonitors, such as those used in ZOLL Medical Corporation's CPR D padz®and Real CPR chest compression monitor, give real time feedback to a CPRprovider, measuring the depth and rate of compressions achieved duringCPR and providing immediate reports of achieved chest compression depthto the CPR provider. This helps the CPR provider achieve the desiredcompression depth and also helps the CPR provider realize when he is toofatigued to provider proper chest compressions. In use, the chestcompression monitor is sandwiched between the chest of a cardiac arrestvictim and the hands of a CPR provider during compressions. These chestcompression monitors are free-floating, and can accurately measure chestcompression depth without reference to any external reference or input.This is described in Halperin, et al., CPR Chest Compression Monitor,U.S. Pat. No. 6,390,996 (May 21, 2002), as well as Palazzolo, et al.,Method of Determining Depth of Chest Compressions During CPR, U.S. Pat.No. 7,122,014 (Oct. 17, 2006). Nonetheless, these chest compressionmonitors can be augmented with reference sensors, to ensure or improveaccuracy when chest compressions are performed on a patient that iscoincidentally subject to gross vertical movements. For example,Palazzolo, et al., Method Of Determining Depth Of Chest CompressionsDuring CPR, U.S. Pat. No. 7,122,014 (Oct. 17, 2006) disclosed a systemincluding a chest compression monitor disposed on the chest of a cardiacarrest victim and a reference sensor disposed elsewhere on the body ofthe cardiac arrest victim or a gurney supporting the cardiac arrestvictim.

For adults, CPR chest compressions are delivered while the patient issupine, supported by a sufficiently rigid surface (a floor, gurney, orhospital bed). For infants, CRP chest compressions are provided with oneof two methods. The preferred method is the two-thumb method, andentails grasping the infants thorax with both hands, placing both thumbsover the sternum (with the fingers supporting the back of the infant)and compressing the sternum with the thumbs. Another method, suggestedfor use by a lone rescuer, is referred to as the two-finger method, andentails compression of the infant's chest with two fingers placed overthe inter-mammary line (superior to the xiphoid process). Compressionsshould be about 1.5 inches (3.8 cm) (one third of the thickness of thethorax of 4.5 inches (11.4 cm), which is rough estimate of infant chestthickness which is of course variable depending on the age of the infantpatient). The chest should be released completely after eachcompression. According to the American Heart Association, the2-thumb-encircling hands technique is preferred over the 2-fingertechnique because it produces higher coronary artery perfusion pressure,results more consistently in appropriate depth or force of compressions,and may generate higher systolic and diastolic pressures.

In another aspect of CPR, active compression-decompression CPR has beensuggested as an adjunct to CPR. Active compression-decompression refersto compression techniques which include some mechanism for activelylifting the chest wall between compression down strokes, rather thanmerely relying on the natural resilience of the chest wall to expand thechest between compressions. Active decompression devices, such asproposed by Steen, Systems and Procedures for Treating Cardiac Arrest,U.S. Pat. No. 7,226,427 (Jun. 5, 2007), use a piston to compress thechest. The piston is driven up and down by a motor. A suction cup on thelower face of the piston is intended to pull the chest wall up with thepiston. Active decompression is not yet recommended for pediatric use.

SUMMARY

The devices and methods described below provide for chest compressionmonitoring during CPR provided to infant cardiac arrest victims,especially where compressions are provided with the two-thumb method.The device includes a chest compression monitor and a reference sensormounted on the tips of an easily deformable open frame which fits aroundthe infant's thorax. The open frame is place around the infant's thorax,with one sensor disposed on the compression point and one sensordisposed on the infant's back, and the CPR provider performs thetwo-thumb compression technique with one sensor trapped between histhumbs and the infant's chest, and the other sensor trapped between therescuer's fingers and the infant's back. The device used to measurechest compression depth can be augmented to provide active decompressionfor infant cardiac arrest victims. The frame which holds the device maybe resilient, such that it forcefully returns to an open position, andthe tips of the frame may be adhesive, such that they adhere to theinfants chest and back, such that upon each release by the CPR provider,the frame exerts a gently expansive force on the infant's thorax.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the two-thumb technique for accomplishing CPRcompressions on an infant.

FIG. 2 illustrates placement of the new chest compression depthmonitoring system on an infant cardiac arrest victim.

FIG. 3 illustrates the two-thumb technique for accomplishing CPRcompressions on an infant while the system of FIG. 2 is installed on theinfant.

FIG. 4 illustrates the frame in isolation.

FIGS. 5A, B and C illustrate the compression frame during compressionsof the infants thorax.

FIG. 6 illustrates a wrap-around frame which can be fitted on an infantcardiac arrest victim.

FIG. 7 illustrates a variation of the frame, applied to infant cardiacarrest victim over the shoulders of the infant.

FIG. 8 illustrates a frame for use in the system which can be easilymodified to adjust the resilience of the frame.

FIG. 9 illustrates a frame for use in the system, which can be adjustedto fit infants of various sizes.

DETAILED DESCRIPTION OF THE INVENTIONS

FIG. 1 illustrates the two-thumb technique for accomplishing CPRcompressions on an infant. The infant is shown supine, supported on asurface. A CPR provider has placed his hands around the infant's thorax,placing his thumbs over the infant's sternum with his fingers wrappingover the axillary area under the infant's arms and around the infant'sback. In this method, the CPR provider squeezes the infant's thorax,with the thumbs pressing on the sternum, to push the sternum toward thespine. These compression should be accomplished at a rate of 100compressions per minute and a depth of 1.5 inches (3.8 cm) (or aboutone-third of the total thickness of the thorax).

FIG. 2 illustrates placement of the new chest compression depthmonitoring system on an infant cardiac arrest victim 1. The systemincludes a first sensor 2 located over the sternum and a second sensor 3located on the back. These two sensors are mounted on a frame 4, which,as illustrated, is a U-shaped frame defining an open space whichaccommodate the infant. The sensors are mounted on the frame such that,with the frame disposed about the infant's thorax, the sensors may beproperly located over the sternum and opposite the sternum on theinfant's back. The sensors are operably connected to an automaticexternal defibrillator (AED) 5 through cable 6. The AED box 5 includes acontrol system, a display and speaker, and a defibrillator. The displayand speaker are operable for providing visual or audio feedback to theCPR provider regarding the depth and rate of the compressions providedby the CPR provider, and comprise means for providing feedback to theCPR provider. The AED also includes an input device, such as a keyboard,soft-keys or touchscreen (which may also be used as the display). Thecontrol system (a computer) is programmed to interpret the accelerationsignals to calculate compression depth and/or velocity (specifically,release velocity), and generate visual displays and/or audio prompts tobe displayed or played to guide the CPR provider. (The control systemalso analyzes ECG signals obtained from ECG electrodes, not shown, todetermine if defibrillating shock should be applied, and may prompt theuser to apply shock or automatically operate the defibrillator to applyshock to the infant patient.) The control system can also be provided ina stand-alone device, without the defibrillator function. The controlsystem comprises at least one processor and at least one memoryincluding program code with the memory and computer program codeconfigured with the processor to cause the system to perform thefunctions described throughout this specification.

FIG. 3 illustrates the two-thumb technique for accomplishing CPRcompressions on an infant while the system of FIG. 2 is installed on theinfant. As in FIG. 2, the frame 4 is disposed about the thorax of theinfant, with the first sensor 2 disposed over the sternum of the infantand the second sensor 3 (see FIG. 2) disposed on or under the back ofthe infant. The rescuer is shown with his/her thumbs over the firstsensor, trapping the first sensor between the rescuer's thumbs and theinfant's sternum, and the fingers of both hands wrapped around theinfant's thorax, preferably trapping the second sensor between thefingers of the rescuer and the back of the infant.

FIG. 4 illustrates the frame in isolation. The frame may take on manyforms, and is illustrated as a U-shaped frame 4, comprising twolaterally extending elements 7 and 8 joined by an arcuate segment 9. Thesensors 2 and 3 are mounted near the tips 10 and 11 of extendingelements, so that they can easily be located with the first sensor 2disposed over the sternum of the infant and the second sensor 3 disposedon or under the back of the infant. The frame construction assuresproper placement of the sensors on the anterior and posterior surface ofthe infant, so that motion signals from each sensor can be used tomeasure the chest wall motion induced by the CPR compressionsaccomplished by the CPR provider, taking into account anyanterior/superior motions of the infant's entire thorax attendant to thetwo-thumbs technique. The frame is preferably resilient and biased to anopen configuration (as large or larger than the thickness of theinfant's thorax), such that after each compression, it resilientlyreturns to an open position, but may instead be merely flexible suchthat upon release of the chest by the CPR provider the frame expands dueto the natural resilience of the infant's thorax. The frame isillustrated as an open U-shaped frame, but may be most any shape usefulto properly locate the sensors above and below the infant's thorax andconvenient to dispose about the infant's thorax. So, for example, theframe may be an oval which completely encircles the thorax. The framemay be provided in various sizes, with each size chosen to suit a rangeof infants and small children of various sizes, or it may be provided insingle size suitable for a wide range of patient sizes.

If the system is intended to impart some expansive force on the chestbetween compression down strokes, during the release phase or upstrokeof a compression, the inner surfaces of the extending segments of aresilient frame, which inner surfaces may include the inner surfaces ofthe sensor assemblies (or housings, if they are discrete from theextending segments), may be covered or coated with an adhesive layersuitable for adhering the extending segments to the thorax of theinfants. The adhesive may be limited to the tips of the extendingsegments, such that only the tips of the extending segments adhere tothe chest wall. With this construction, with each release of compressionforce, the resilient expansion of the frame will exert expansive forceon the chest wall, and provide a degree of active decompression betweeneach compression.

FIGS. 5A, B and C are cross sections of the frame, illustrating theaction of the frame on the thorax of the infant. As shown in FIG. 5A,the frame is slipped over the infant's chest, such that the anteriorsensor 2 is disposed directly over the sternum 12, and the posteriorsensor 3 is located under the spine 13. The CPR provider squeezes theinfant's chest, using the two-thumbs technique, to achieve thecompressed state illustrated in FIG. 5B. FIG. 5B represents thecompression stroke or compression phase of the compression cycle. Uponrelease, the infant's chest will expand, as shown in FIG. 5C, to itsoriginal thickness H. Where the interior surfaces of the extendingsegments are adhesive, the resilient expansion of the frame lead to anexpansive force applied to the chest, which hastens the expansion of thechest during the release phase of the compression cycle.

FIG. 6 illustrates a version of the frame which wraps entirely aroundthe infant cardiac arrest victim. In FIG. 6, the frame 4 may be providedin a length exceeding the circumference of the infant, and sufficient toentirely surround the infant's thorax (practically, the wrap aroundframe will be provided in a single length long enough to surroundinfants of various sizes). As with the frames of the earlier figures,the frame of FIG. 6 is resiliently biased to open to a circumferencelarger than the circumference of the infant. The frame may have aninitial configuration which is substantially flat, in which case it isfolded up and around the infant's thorax as shown, and adjusted toobtain a close fit with the infant's thorax before compressions areinitiated. The frame may instead have an initial configuration which issubstantially circular, in which case it is spread open to accommodatethe infant's thorax and adjusted to obtain a close fit with the infant'sthorax before compressions are initiated. The anterior sensor 2 may bereleasably fixed to the frame, with hook and loop fastener or otherfastener, so that it can be relocated to the infant's sternum when theframe is adjusted to fit about the infant.

FIG. 7 illustrates a variation of the frame, applied to infant cardiacarrest victim over the shoulders of the infant. The frame of FIGS. 2through 4 can of course be fitted over one shoulder of the infant, atthe option of the CPR provider. The frame 14 of FIG. 7 comprises a frontportion 15 and back portion 16, with an opening between the two toaccommodate the infant's head. From the side or lateral aspect, theframe is U-shaped. As with the frame of FIGS. 2 through 4, this framemay be resilient and biased to an open position, with the distancebetween the sensors in the open, relaxed configuration being slightlygreater than the anterior-posterior thickness of the infant's thorax.The sensors 2 and 3 are mounted on the frame, with the anterior sensor 2mounted on the front portion and the posterior sensor 3 mounted on theback portion. As illustrated, viewed from the front or anterior aspect,the front portion is V-shaped, with the vertex 17 of the V, where theanterior sensor 2 is located, disposed over the sternum of the infant.The posterior sensor 3 located directly below the anterior sensor, onthe back portion and located at the back of the infant. The vertex ofthe V serves as an easily recognizable landmark for the user whenapplying the frame to the infant, but the frame may be made in otherconfigurations that permit the frame to be slipped over the infant'shead (for example, a bib or pinafore), and provide for locating theanterior sensor over the infant's sternum.

The frame can be provided in a single size chosen to fit most infantssubject to the two-thumb technique, and configured with a resilience andexpansive force suitable for applying active compression/decompressionfor most infants, or the frame can provided in a variety of sizes,leaving to a CPR provider to select an appropriate size and/orresilience at the point of use, or adjust size and/or resilience of theframe at the point of use when the size of the actual patient is known.Should it be desirable to adjust these properties, the frame can bemodified as illustrated in FIGS. 8 and 9. FIG. 8 illustrates a frame foruse in the system which can be easily modified to adjust the resilienceof the frame. The frame 21 holds the anterior and posterior sensors 2and 3 at the tips of anterior and posterior extending elements 7 and 8.The frame 21 is resilient, and manufactured to exert a first level ofexpansive force when released from compression. The frame comprises oneor more additional layers 22, 23 and 24, which are also resilient. Theadditional layers are secured to the underlying layers with adhesive ora mechanical interlock, such that they are releasable secured tounderlying layers and may be removed easily by the CPR provider. Toadjust the resilience of the frame, one or more releasable layers may beremoved, thus weakening the frame and reducing its resilience.

FIG. 9 illustrates a frame for use in the system, which can be adjustedto fit infants of various sizes. The laterally extending segments 7 and8 are connected to each other through an expandable ratcheting mechanism25. The ratcheting assembly may be used to expand or collapse thelaterally extending segments 7 and 8 to size the device to a particularinfant cardiac arrest victim. As with the U-shaped frames illustratedabove, the sensors 2 and 3 are disposed within or on the tips of theextending segments.

The sensors may include any sensor technology suitable for determiningcompression depth. Accelerometers may be used, as described in Halperin,U.S. Pat. No. 6,390,996 and Palazzolo, U.S. Pat. No. 7,122,014. In thiscase, the anterior sensor may be an accelerometer-based chestcompression monitor as described in Halperin and Palazzolo, and theposterior sensor can be a reference accelerometer or anotheraccelerometer-based chest compression monitor. The accelerometers arecapable of producing acceleration signals corresponding to theacceleration of the chest and the acceleration of the back, and thecontrol system is operable to integrate the acceleration signal receivedfrom the accelerometers, integrating and combining those signals todetermine the depth of chest compression and produce a measured depthsignal. The control system is also programmed to report the measureddepth to the CPR provider through the display or audio output, orcompare the measured depth signal to a desire depth of compression andreport to the CPR provider whether the achieved depth of compressionmeets or fails to meet the desired depth. Velocity sensors may also beused, in which case the control system is programmed to process thevelocity signal received from the velocity signals to achieve the sameends. Also, the control system may be programmed to process theacceleration signals to determine the compression velocity, releasevelocity, and compression rate to produce corresponding signals, andprovide reports and feedback to the CPR provider regarding theseparameters.

Magnetic motion sensors, such as those which use an electromagneticsource and sensor, described in Geheb, et al., Method and Apparatus forEnhancement of Compressions During CPR, U.S. Pat. No. 7,220,235 (May 22,2007) and Centen, et al., Reference Sensor For CPR Feedback Device, U.S.Pub. 2012/0083720 (Apr. 5, 2012), may also be used to determinecompression depth. In this case, the one sensor is a magnetic fieldsensor, and the other sensor is replaced by a magnetic field generator(a permanent magnet or an electromagnet), and the control system isoperable to receive and process distance information from theelectromagnetic sensor to determine compression depth, release velocity,and compression rate. These and any other means for determiningcompression depth, compression rate, and release velocity may be used.

The control system is programmed to receive signals corresponding tomotion of the chest wall and motion of the thorax (motion of the back,as sensed by the sensor 3, and determine the depth of compressionachieved during CPR based on those signals. (In the magnetic sensingembodiment, the control system is programmed to determine the depth ofcompression achieved during CPR based signals from the magnetic fieldsensor.) The control system is programmed to generate a signalcorresponding to the determined chest compression depth which may beused to provide a display indicating achieved chest compression, or maybe used by other equipment. The control system is further programmed tocompare the determined depth of compression with predetermined desiredchest compression goals, and provide feedback to a CPR providerregarding the adequacy of chest compression depth, including whetherachieved chest compression depth is inadequate, adequate, or excessiveas compared to the predetermined goals. The feedback can include audioor visual prompts to compress more deeply, prompts to compress at afaster or slower rate, and prompts to quickly and completely release thechest of the patient after each compression. The feedback can alsoinclude haptic feedback, provided when compression depth is adequate,inadequate, or excessive, through vibrators disposed on the frame.

The system can be adapted to determine an initial measurement of thepatient's chest. The sensors mentioned above may be used, or additionalsensors may be added to the frame, to measure the patient's chest priorto the start of chest compressions. This information can be use toadvise a CPR provider to limit expansive motion of the frame duringrelease (to limit the active decompression) (limiting the expansivemotion of the frame during release can be accomplished merely by holdingthe frame between compressions, and not allowing it to fully expand),and to advise the CPR provider regarding the adequacy of chestcompressions based on the size of the patient. The distance between thesensors 2 and 3 can be determined, using signals from the sensors, whereapplicable. For example, where the sensors are a magnetic field sensorand a magnetic field generator, the position of the magnetic sensor inthe magnetic field generated by the magnetic field generator can bedetermined.

Additional sensors may be used to size the patient. Distance sensors andproximity sensors at the tips of the frame, near sensor 2, for example,can determine the distance from the frame tip to the patient, andthereby calculate the size of the patient. This system may requireoperator input, to inform the system when the frame is disposed aboutthe patient such that the bottom frame tip and sensor 3 are in placebelow the patient, so that the control system can then calculate thepatient's chest height based on the known distance between the frametips and the measured distance between the upper frame tip and the chestwall of the patient. In another system, strain sensors disposed on orwithin the frame can be used to determine the shape of the frame, andthus the distance between the frame tips. For example, a shapemonitoring cable (item 19 in FIG. 4 comprising linear arrays of fiberBragg gratings may be disposed on or within the frame, and a controlsystem may operate a light source and light sensors to determine theshape of the frame. This system may require operator input, to informthe system when the frame is disposed about the patient such that thebottom frame tips and sensor 2 and sensor 3 are in in contact with thepatient, so that the control system can then calculate the patient'schest height based on the shape of the frame as determined by the shapemonitoring cable. Shape monitoring cables suitable for use in thisembodiment may also include piezo-electric strain gauges and other formsof strain gauges.

For the frame of FIG. 9, an optical, magnetic or capacitive encoder orother position sensor 27 can be used to determine the position ofratcheting segments relative to each other, and from this informationthe control system can determine the distance between the tips and thechest height of the patient. Again, with operator input informing thesystem when the frame is disposed about the patient such that the bottomframe tips and sensor 2 and sensor 3 are in in contact with the patient,the control system can then calculate the patient's chest height basedon the encoder reading. Thus, for the initial determination of the sizeof the patient, sensors mounted on the frame tips, encoders disposed onan adjustable portion of the frame, a shape monitoring cable disposed onthe frame, and any other suitable means of determining the distancebetween the frame tips can be used, in conjunction with input from theCPR provider indicating that the frame tips are in close proximity tothe patient's thorax.

In each case, the initial measurement of the size of the patient'sthorax can be use by the control system to select advisory parameters,such as the amount of compression desired, and the amount of activedecompression desired, for the patient based on patient size, andgenerate advisory prompts to the CPR provider based on patient size. Thecompression depth targets for infants should be about ⅓ of the infant'schest height, and the appropriate chest compression goals can beselected by the control system programmed to calculate the chestcompression goals based on the measured size of the patient. Thus, forCPR compressions performed on small children, the control system wouldbe programmed to provide a positive advisory (that compression areadequate) or a negative advisory (that compression are excessive, oractive decompression too expansive) for small compressions and activedecompressions, and also programmed to provide a positive advisory (thatcompression are adequate) or a negative advisory (that compression areexcessive, or active decompression too expansive) for slightly largercompressions and active decompressions for CPR performed on a largerchild.

In use, a CPR provider will place the frame around the thorax of aninfant cardiac arrest victim, with one sensor on the victim's chest,over the victim's sternum, and the second sensor under the infant'sspine. The CPR provider will then grasp the infant's thorax with bothhands, placing his thumbs over the infant's sternum and extending hisfingers around the thorax, in the two-thumbs position. The CPR providerwill perform CPR compressions, using the two-thumbs technique, pressingdown on the chest, keeping the anterior sensor between his thumbs andthe victim's chest, so that the sensor moves up and down in fixedrelation with the patient's chest, and keeping the posterior sensorbetween his fingers and the victim's spine, or at least keeping theposterior extending element between his fingers and the patient's backso that the posterior sensor moves up and down in fixed relation withthe patient's back. The CPR provider will operate an associated controlsystem, and energize the sensors, to analyze the sensor signals todetermine chest compression depth, velocity of the compression monitor(including release velocity), and the rate of compression, compare thedetermined chest compression depth, release velocity and/or compressionrate to the desired values, and operate an output device to provideprompts indicating whether the determined chest compression depth,release velocity and/or compression rate meets or fails to meet thedesired values. The control system may also be operated to compare themeasured depth of compression to a desired depth of compression andreport to the CPR provider whether the achieved depth of compressionmeets or fails to meet the desired depth. Prior to the start ofcompressions, the CPR provider may optionally bring the anterior frameand posterior frame into contact with the body, and provide input to thecontrol system that the anterior frame and posterior frame are incontact with the body.

The frame may be used to perform CPR compressions, including activecompression/decompression, with or without the compression depthmonitoring components of the system. The frame, with an adhesive surfaceon at least a portion of the interior surface of the anterior segment,can be installed about the thorax of a patient such that the adhesivesecures the anterior segment to the patient's chest wall, over thesternum (that is, the preferred compression point). With the frameinstalled, CPR compressions are performed. Upon release of eachcompression, the resilient frame will resiliently expand toward its openconfiguration, thereby imparting some expansive force on the chest wall.If the patient is prone on a supportive surface, only the anteriorsegment need be adhesive. If the patient is held up, or prone on a softsurface, the posterior segment interior surface may be adhesive as well.This method may be used on adults and pediatrics as well as infants.

When used to provide CPR compressions with activecompression/decompression the method entails providing the frame havingan anterior segment and a posterior segment, and sized and dimensionedto fit at least partially around the thorax of the cardiac arrest victimwith adhesive on a portion of the anterior segment is adhesive and,optionally, on the posterior segment, and installing the frame about thethorax of a cardiac arrest victim such that the adhesive secures theanterior segment to the cardiac arrest victim's chest wall. Afterinstallation, the CPR provider performs CPR chest compressions on thecardiac arrest victim, allowing the frame to expand between compressionsto provide active decompression, with the resilience of the frame actingto restore the frame toward its relaxed opened position and thus exertupward pulling force on the thorax.

While the preferred embodiments of the devices and methods have beendescribed in reference to the environment in which they were developed,they are merely illustrative of the principles of the inventions. Thoughillustrated for use with infants and the two-thumb compressiontechnique, the devices may be used the two-finger technique, and thedevices may sized and dimensioned for adult use, and used in otherwisestandard CPR compressions. The elements of the various embodiments maybe incorporated into each of the other species to obtain the benefits ofthose elements in combination with such other species, and the variousbeneficial features may be employed in embodiments alone or incombination with each other. Other embodiments and configurations may bedevised without departing from the spirit of the inventions and thescope of the appended claims.

We claim:
 1. A device for assisting resuscitation of a victim during CPRchest compressions comprising: an anterior sensor disposed on ananterior segment, said anterior segment configured to be held adjacentto an anterior surface of the victim and said anterior sensor operableto produce a first signal corresponding to motion of the anteriorsurface during compressions; a posterior sensor disposed on a posteriorsegment, said posterior segment configured to be held adjacent to anposterior surface of the victim and said posterior sensor operable toproduce a second signal corresponding to motion of the posterior surfaceduring compressions; a control system operable to receive the firstsignal corresponding to motion of the anterior surface and the secondsignal corresponding to motion of the posterior surface and determinecompression depth therefrom; and a feedback device configured to provideCPR advisory prompts to a rescuer based on the calculated compressiondepth, velocity or rate; wherein the anterior segment and posteriorsegment are configured to provide active decompression between CPR chestcompressions.
 2. The device of claim 1, wherein the anterior segment isjoined to the posterior segment, such that the anterior segment andposterior segment are resiliently biased to open to a configurationlarger than a thickness of the victim's chest.
 3. The device of claim 1,wherein the anterior segment is joined to the posterior segment, suchthat the anterior segmetn and posterior segment are resiliently biasedto open to a configureation larger than the circumference of the victim.¶27.
 4. The device of claim 1 wherein: the posterior sensor is operableto detect acceleration of the posterior surface, and the the controlsystem operable to determine depth, velocity or rate of CPR chestcompressions from acceleration data obtained from the posterior sensorand data from the anterior sensor during CPR chest compressions.
 5. Thedevice of claim 1 wherein: the anterior sensor is operable to detectacceleration of the anterior surface, and the the control systemoperable to determine depth, velocity or rate of CPR chest compressionsfrom acceleration data obtained from the anterior sensor and data fromthe posterior sensor during CPR chest compressions.
 6. The device ofclaim 1 wherein: the posterior sensor is operable to detect velocity ofthe posterior surface, and the the control system operable to determinedepth, velocity or rate of CPR chest compressions from velocity dataobtained from the posterior sensor and data from the anterior sensorduring CPR chest compressions.
 7. The device of claim 1 wherein: theanterior sensor is operable to detect velocity of the anterior surface,and the the control system operable to determine depth, velocity or rateof CPR chest compressions from velocity data obtained from the anteriorsensor and data from the posterior sensor during CPR chest compressions.8. The device of claim 1, wherein the control system is further operableto compare the measured depth of compression to a desired depth ofcompression and report to a CPR provider whether the achieved depth ofcompression meets or fails to meet the desired depth.
 9. The device ofclaim 1 wherein the control system is operable to determine the size ofthe cardiac arrest victim based on the distance between the anteriorsegment of the frame and the chest wall and provide feedback regardingthe performance of chest compressions based on the determined size ofthe cardiac arrest victim.
 10. The device of claim 1 wherein: theanterior segment is configured to adhere to the anterior surface of thevictim.
 11. The device of claim 1 wherein: one of the posterior sensorand the anterior sensor is operable to detect a magnetic field andproduce a signal corresponding to motion through a magnetic field; andthe other of the posterior and the anterior sensor is operable to sensethe magnetic field; and the control system operable to determine depth,velocity or rate of CPR chest compressions from the signal correspondingto motion through the magnetic field during CPR chest compressions. 12.A method of administering CPR chest compressions on a cardiac arrestvictim, said cardiac arrest victim characterized by a thorax and ananterior chest wall, said method comprising the steps of: disposing aframe sized and dimensioned to fit at least partially around the thoraxof the cardiac arrest victim, said frame having an anterior segment anda posterior segment, an anterior sensor disposed in or on the anteriorsegment of the frame, said anterior sensor capable of producing a signalcorresponding to motion of the chest wall during compressions; aposterior sensor disposed in or on the posterior segment of the frame,said anterior sensor capable of producing a signal corresponding tomotion of the thorax during compressions; performing CPR compressions onthe cardiac arrest victim; operating a control system to receive thesignal corresponding to motion of the chest wall and the signalcorresponding to motion of the thorax and determine the depth of chestcompressions therefrom, and provide audio or visual feedback to a CPRprovider.
 13. The method of claim 12 further comprising the step of:operating the control system to provide prompts to a CPR providerregarding the depth of compression.
 14. The method of claim 12 furthercomprising the step of: operating the control system to compare thedetermined depth of compression to a desired depth of compression andreport to a CPR provider whether the determined depth of compressionmeets or fails to meet the desired depth.
 15. The method of claim 12further comprising the step of: bringing the anterior segment andposterior segment into contact with the thorax, and providing input tothe control system that the anterior segment and posterior segment arein contact with the thorax.
 16. The method of claim 12, wherein the stepof performing CPR compressions further comprises the steps of: trappingthe anterior sensor between the CPR provider's hands and the victim'schest wall, and performing CPR compressions with the anterior sensordisposed between the CPR provider's hands and the victim's chest wall.17. The method of claim 12, wherein the step of performing CPRcompressions further comprises the steps of: grasping the cardiac arrestvictim's thorax with both hands of the CPR provider, with the CPRprovider's thumbs over the sternum and the CRP provider's fingersextending around the thorax of the victim, trapping the first sensorbetween the CPR provider's thumbs and the victim's chest wall, andtrapping the second sensor between the CPR provider's fingers and thevictim's spine, and performing CPR compressions with a two-thumbstechnique.
 18. The method of claim 12, further comprising the step of:adhering the frame to the cardiac arrest victim's thorax, and allowingthe frame to expand between compressions to provide active decompressionof the thorax.
 19. A method of performing CPR compressions, includingactive compression/decompression, said method comprising: providing aframe sized and dimensioned to fit at least partially around the thoraxof the cardiac arrest victim, said frame having an anterior segment anda posterior segment, wherein at least a portion of the anterior segmentis adhesive; installing the frame about the thorax of a cardiac arrestvictim such that the adhesive secures the anterior segment to thecardiac arrest victim's chest wall; performing CPR chest compressions onthe cardiac arrest victim.